Pneumatically operated, underground piercing tools are commonly used to install wire, conduit and tubing under a roadway, sidewalk, etc. The use of these devices reduces the need for excavating or trenching and, hence, provide a cost effective method for installing utility lines, cable, etc. in developed areas. This type of tool eliminates the need for excavating through hard landscape items that obstruct the path of the line or conduit being installed. An example of this type of piercing tool is fully disclosed in U.S. Pat. No. 4,662,457 which is hereby incorporated by reference. As fully explained in that patent, a striker mechanism which is operated by pressurized air, either repeatedly impacts an anvil mounted at the nose of the tool in order to move the tool forwardly, or repeatedly impacts an abutment located at the rear of the tool in order to move the piercing tool rearwardly, i.e., to withdraw the tool from the bore hole. U.S. Pat. Nos. 3,865,200 and 5,465,797 illustrate other examples of piercing tools that have other types of striking elements i.e. percussion tips located at a forward end of the tool.
The piercing tool disclosed in the '457 patent has enjoyed commercial success. However, it has become desirable to improve the reliability and life of these types of tools, and to reduce and simplify maintenance. In the type of tool to which this invention pertains, the various components that make up the tool assembly are connected together using threaded connections. The threaded connections facilitate both assembly during the manufacture of the tool and facilitate disassembly when the tool requires maintenance. It has been found, however, that these threaded connections can be a source of failure during operation of the tool. These threaded connections experience substantial impact loads as the internal striker repeatedly strikes either the anvil or the rear abutment. These failures can be further precipitated by operating the tool at higher than recommended air pressures and/or operating the tool outside its intended parameters.
It is, therefore, desirable to provide a tool of this type that can be manufactured at reduced cost, but with improved reliability while at the same time facilitating its maintenance and repair.